1. Field of the Invention
The present invention relates to a General Packet Radio System (GPRS) and more particularly to a data transmission method in the GPRS.
2. Background of the Related Art
A GPRS is an overlay network system implemented on a global system for mobile communications (GSM) network, which is a circuit switching-based two-generation radio communication network standard adapted by GPRS for packet data transmissions. In order to transmit packet-based data on the GSM network, a fresh network factor, an interface, and a protocol are required to process packet traffic.
The GPRS is logically implemented by adding two network nodes as core network (CN) factors of the GSM. The first node is a serving GPRS Support Node (SGSN) and the second node is a gateway GPRS Support Node (GGSN). In addition to these nodes, a packet control unit (PCU) for processing a packet traffic should be installed in a base station controller (BSC), and software upgrading should also be performed.
In the GPRS system constructed as described above, voice or data traffic transmitted from a GPRS terminal is transmitted to a BTS through an air interface and then transmitted from the BTS to the BSC in the same manner. However, at the output side of the BSC, the traffic is divided into voice traffic which is transmitted to a mobile switching center (MSC) as standard GSM traffic and data traffic which is transmitted to the SGSN through the PCU.
The GPRS uses a physical channel called a temporary block flow (TBF) for data transmission between the terminal and a network. The TBF is set when there is an LLC PDU transmission request by an upper layer of the terminal in a packet idle mode. When the TBF is set, the terminal is switched to a packet transfer mode.
The LLC PDU transmission service is provided in an RLC acknowledged mode and an RLC unacknowledged mode, and when the LLC PDU transmission in uplink and downlink directions is terminated, the corresponding TBF is released. As the TBF is released in the packet transfer mode, the terminal returns to the packet idle mode.
FIG. 1 shows a protocol layer adopted in the GPRS system. As shown, a data link layer consists of a logical link control (LLC), radio link control (RLC), and medium access control (MAC) sub-layers. These sub-layers provide a service on an upper layer protocol and receives a service from a physical layer. The LLC sub-layer provides a logical channel ensuring reliability between two peer entities, while the RLC sub-layer positioned below the LLC sub-layer segments a to-be-transmitted LLC protocol data unit (PDU) to RLC/MAC block and reassembles received RLC/MAC block. The MAC sub-layer positioned below the RLC sub-layer allows a plurality of mobile terminals to share a physical channel.
The RLC/MAC block is classified into an RLC data block and an RLC/MAC control block in the acknowledged mode. The RLC/MAC control block has priority over the RLC data block. The RLC/MAC block consists of an MAC header and an RLC data block which includes an RLC header, an RLC data unit, and spare bits.
FIG. 2 shows a format of an uplink RLC data block containing an MAC header adopted for the GPRS system in accordance with a related art. The MAC header consists of a payload type field indicative of a type of data carried in the RLC/MAC block, a countdown value field indicative of a countdown value (CV) that the terminal transmits in order for a network to calculate the current number of RLC data blocks remaining for the uplink TBF, a stall indicator (SI) bit indicative of whether an RLC transmission window of the terminal can advance, and a retry (R) bit indicative of whether the terminal has transmitted a CHANNEL REQUEST message or a PACKET CHANNEL REQUEST message more than once during the latest channel access.
An uplink RLC data block includes a spare bit set to ‘0’, an PFI indicator (PI) indicative of whether there is a packet flow identifier (PFI), an optional item, a TLLI indicator (TI) bit indicative of whether there is a temporary flow identity (TFI) field for checking a TBF where the RLC data block belongs or whether there is a TLLI field, an optional item, a BSN field indicative of a block sequence number (BSN), a length indicator (LI) for determining a boundary of LLC PDUs of the RLC data block, a more (M) bit indicative of whether there is a following LLC PDU in the RLC data block, and an extension (E) bit indicative of whether there is an optional octet in the RLC PDU.
In the uplink TBF operation process, the terminal transmits the RLC/MAC block through each allocated uplink data block, and the network sends a PACKET UPLINK ACK/NAK message to the terminal as necessary. If a transmission status variable V(S) is equal to the sum of an acknowledge state variable V(A) and a transmit window size (WS) modulo SNS (that is, V(S)=V(A)+WS modulo SNS), the terminal judges that the transmit window is in a stall state. Then, the terminal sets stall indicators (SI) of every transmitted uplink RLC block to ‘1’ so as to inform the network of the stall state until the transmit window gets out of the stall state.
However, in the case that the terminal informs the network of the stall state using the following data blocks after the transmit window is in stall state, the terminal keeps re-transmitting the RLC data blocks which have not been acknowledged from the network until it receives a PACKET UPLINK ACK/NACK message from the network and gets out of the stall, and if the stall state is prolonged, radio resources are wasted.
The above references are incorporated bit reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.